1. Field of the Invention
The present invention relates to the impeller of the centrifugal compressor provided in the turbochargers for vehicle use, marine use and so on; the present invention especially relates to the blade geometry regarding the splitter blade arranged between adjacent full blades, the blade geometry being related to the splitter blade in the area of fluid inlet part.
2. Background of the Invention
The centrifugal compressor used as the compressor part of the turbocharger for vehicle use, marine use and so on gives kinetic energy to the working fluid inhaled in the centrifugal compressor, via the rotational movement of the impeller; further, the centrifugal compressor delivers the fluid outside of the compressor toward the radial direction so as to increase the pressure of the fluid by use of the centrifugal force given to the fluid. It is required that the operating range of the centrifugal compressor be wide enough to keep the high pressure ratio and the high efficiency in the operation range. In order to meet this requirement, the impeller 05 is often provided with the splitter blade 03 between the adjacent full blades 01 in the impeller, as shown in FIG. 9; further, various ideas regarding the blade geometry have been proposed.
As shown in FIG. 9 and FIG. 10 that shows a part of the cross-section along a radial direction in FIG. 9, in the impeller 05 provided with the splitter blades 03, a full blade 01 and a splitter blade 03 are arranged in turn on the surface of the hub 07; in general, the splitter blade 03 is formed by simply cutting the a part of the full blade on the fluid flow upstream side.
As shown in FIG. 11 (that shows an A-A cross-section indicated in FIG. 10), in relation to the general splitter blade 03, the leading edge LE2 of the splitter blade 03 is arranged at a location of a predetermined distance from the leading edge LE1 of the full blade 01, on a downstream side from the leading edge LE1; the trailing edge TE of the splitter blade 03 as well as the full blade 01 is arranged at a location of a predetermined distance from the leading edge LE1 of the full blade 01, the predetermined distance regarding the splitter blade agrees with that regarding the full blade. Thereby, the leading edge blade angle θ (i.e. the angle formed by the axial direction G regarding the impeller and the blade slope direction regarding the splitter blade at the leading edge thereof) of the splitter blade 03 is set so that the direction of the leading edge blade angle θ corresponds to the angles θ of the slopes of the full blades at the leading edge location of the splitter blade (cf. FIG. 2).
However, in the case where the geometrical shape of the splitter blade is simply formed by removing a part on the flow upstream side of the full blade 01 from the whole full blade, there arises a difference between the throat area A1 of the flow passage on the blade pressure surface side Sa of the full blade and the throat area A2 of the flow passage on the blade suction surface side Sb of the full blade; and, the throat area A1 becomes than the throat area A2 (A1<A2). Accordingly, unevenness is developed with regard to both the fluid flows. Thus, there arises the difference between the flow rate of the fluid flow on the blade pressure surface side and the fluid flow on the blade suction surface side; it becomes difficult to evenly impart the fluid flow; it becomes difficult to equalize the blade load for all the full blades as well as all the splitter blades. And the fluid passage dissipation loss in each fluid passage increases; thus, it becomes difficult to improve the impeller efficiency (the compression efficiency regarding the impeller).
Hence, Patent Reference 1 (JP1998-213094) discloses a contrivance in which, as shown in FIG. 12, the leading edge blade angle θ of the splitter blade 09 is increased to an angle (θ+Δθ); namely, the angle θ is increased by an angle increment Δθ toward the flow inlet direction F from the axial direction. In other words, by bringing the leading edge side of the splitter blade close to the blade suction surface side Sb, the throat area A1 of the flow passage on the blade pressure surface side of the full blade is made equal to the throat area A2 of the flow passage on the blade suction surface side of the full blade (A1=A2).
Further, Patent Reference 2 (JP3876195) discloses a contrivance that the flow entering part of the splitter blade 09 is leaned toward the blade suction surface side of the full blade.
In a case where the leading edge blade angle θ of the splitter blade 09 is increased to an angle (θ+Δθ) according to the disclosure of Patent Reference 1 (as depicted by FIG. 12), however, there is apprehension that the fluid flow around the leading edge part where the slope of the splitter blade 09 is increased is separated from the blade; and, there is apprehension that the fluid flow along the blade suction surface side Sb of the full blade is separated from the blade. Further, even when the throat area A1 of the flow passage on the blade pressure surface side of the full blade and the throat area A2 of the flow passage on the blade suction surface side of the full blade are equalized (i.e. A1=A2), the velocity of the flow in one of the flow passages not the same as the velocity of the flow in the other flow passage; thus, it becomes difficult to equalize the flow rate through the one passage and the flow rate through the other passage.
In other words, the flow rate through the one passage becomes different from the flow rate through the other passage; thus, the fluid entering the space between the adjacent full blades 01 is imparted into the two flow passages so that the fluid flow of higher speed mainly streams through the passage on the blade suction surface side; thus, even when the cross section areas of both the flow passages on both the sides of the splitter blade 09 are geometrically equal to each other, the flow rate of the fluid streaming the flow passage on the blade suction surface side becomes greater than the flow rate of the fluid streaming the flow passage on the blade pressure surface side, in response to the increased flow speed increment. Thus, there arises the difference between the flow rate of the fluid flow on the blade pressure surface side and the fluid flow on the blade suction surface side; it becomes difficult to evenly impart the fluid flow; it becomes difficult to equalize the blade load for all the full blades as well as all the splitter blades. And the fluid passage dissipation loss in each fluid passage increases; thus, it becomes difficult to improve the compression efficiency regarding the impeller.
Under the circumstances as described above, Patent Reference 3 (JP2002-332992) discloses another technology. As shown in FIG. 13, according to the disclosure of Patent Reference 3, the leading edge blade angle θ of the splitter blade 11 is unchanged, and the leading edge (part) is expressly shifted toward the blade suction surface side so that throat area A1 is greater than the throat area A2 (i.e. A1>A2). In this way, the technology disclosed by Patent Reference 3 intends to equalize the flow rates of the fluid streaming through both the sides of the splitter blade 11.